But it should be easier if you find out what bug is it.
Short answer for test ( please check my last messages with some details about a part of tests i've done);
SIBO test = lactulose breath test . It's usefull cause it tells you have fermentation in the gut but is not specific - dont tell what you have.
but its a good start !
please check dr.Myhill website in uk "Fermetation in the gut" you'll find very usefull information. long but worth it. unfortunately I could not work with this lady cause she wans't available :(.
what kind of symptoms does your kid have?
maybe its not SIBO (bacterial) maybe its protozoa like...